Abstract
The uptake and metabolism of cobalamin (Cbl) has been studied in L-1210 murine leukemia cells propagating in vitro. Extracellular Cbl (protein bound and free) and intracellular Cbl (protein bound and free) were determined after culturing L-1210 cells in the presence of [ 57Co]cyanocobalamin (CN-Cbl) bound to transcobalamin II (transcobalamin, TC). The intracellular pool of free [ 57Co]Cbl increased during the first 24 h of culture and a substantial fraction of this free pool was effluxed from the cell to the medium. Upon depletion of extracellular TC-[ 57Co]CN-Cbl, the intracellular concentration of free Cbl decreased as did the efflux of Cbl to the medium. Internalized [ 57Co]CN-Cbl was converted to hydroxocobalamin (OH-Cbl), methylcobalamin (Me-Cbl) and 5′-deoxyadenosylcobalamin. These Cbl forms were found in both soluble (cytoplasmic) and insoluble (membrane) fractions. Intracellular protein-bound [ 57Co]Cbl fractionated with methionine synthase (MS) and methylmalonyl-CoA mutase (MU) activity. The major form of Cbl associated with the two enzymes was OH-Cbl. Cells propagated in medium containing N 5-methyltetrahydrofolate and homocysteine showed a substantial increase in MS activity which paralleled the increase in the intracellular concentration of Me-Cbl and the Cbl bound to the enzyme.
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
